Field
Embodiments of the invention generally relate to pyrometry during thermal processing of semiconductor substrates. More specifically, embodiments of the invention relate to a pyrometry filter for a thermal process chamber.
Description of the Related Art
Rapid Thermal Processing (RTP) is a well-developed technology for fabricating semiconductor integrated circuits. RTP is a process in which the substrate is irradiated with high intensity optical radiation in an RTP chamber to quickly heat the substrate to a relatively high temperature to thermally activate a process in the substrate. Once the substrate has been thermally processed, the radiant energy is removed and the substrate cools. RTP is an energy efficient process because the chamber in which the RTP is performed is not heated to elevated temperature required to process the substrate. In an RTP process, only the substrate is heated. Thus, the processed substrate is not in thermal equilibrium with the surrounding environment, namely the chamber.
The fabrication of integrated circuits involves may steps of depositing layers, photolithographically patterning the layers, and etching the patterned layers. Ion implantation is used to dope active regions in the substrate. The fabrication sequence also includes thermal annealing of the substrate for many uses, such as curing implant damage and activating dopants, crystallization, thermal oxidation and nitridation, silicidation, chemical vapor deposition (CVD), vapor phase doping, and thermal cleaning among others.
Although annealing in early stages substrate processing technology involved heating multiple substrate for long periods in an annealing oven, RTP has been increasingly used to satisfy ever more stringent requirements for processing substrates with increasingly smaller circuit features. RTP is typically performed in a single substrate chamber by irradiating a substrate with light from an array of high intensity lamps directed at the front face of the substrate on which the integrated circuits are formed. The radiation is at least partially absorbed by the substrate and quickly heats the substrate to a desired high temperature. The desired temperatures generally are above 600° C. and in certain applications, above 1000° C. The radiant heating can be quickly activated and deactivated to controllably heat the substrate over short time intervals, such as between about 60 seconds and about 1 second.
During certain processes, lower temperatures (i.e. less than 400° C.) may be required. An example of using lower temperatures includes forming silicides on a substrate. The quality and performance of processing a substrate in a chamber depends in part on the ability to provide and maintain an accurate temperature of the substrate. Temperatures of a substrate in a processing chamber are usually measured by a pyrometer, which measures temperature within a bandwidth of wavelengths. Radiation that is within the radiation pyrometer bandwidth, and that originates from the heating source, can interfere with the interpretation of the pyrometer signal if the radiation is detected by the pyrometer. “Leaking” heat radiation, radiation not intended to be measured by the pyrometer, can interfere with the pyrometer reading and provide an inaccurate temperature measurement. Moreover, not all substrates are opaque at the pyrometer bandwidth, especially when the substrate is maintained at lower temperatures. Objects at low temperatures emit thermal radiation at lower intensity than objects at high temperatures. The weak thermal emission of low temperature objects can be overwhelmed by other heat signals and lost.
Accordingly, what is needed in the art are improved systems to measure temperatures accurately with a pyrometer. More specifically, what is needed is a pyrometry filter for a thermal processing chamber.